Ultra high frequency oscillator



Oct. 1, 1940. R. H. GEORGE ULTRA HIGH FREQUENCY OSCILLATOR Filed July 25, 1939 gas $1 In; INV EN T OR.

1?. H. GEORGE ATTORNEY.

Patented on. 1. 1940 UNITED STATES PATENT osrica 1 ULTRA HIGH FREQUENCY OSCILLATOR Roscoe H. George,

Application July 25,

24 Claims.

This invention relates to an improvement in oscillators and particularly in oscillators for developing ultra high frequencies.

Heretofore, ultra high frequency oscillators of various designs have been used but such oscillators have had the disadvantage of being unstable under operating conditions and furthermore, such oscillators have been more or less limited in the available power output. These previously used ultra high frequency oscillators have not been self-contained, and have been so constructed that cooling of the oscillators other than by natural radiation and conduction of heat was irn-. practical or impossible. Moreover, in previously used oscillators the frequency of oscillation was controlled by external parameters or tuned circuits. and the presence of these circuits frequently caused a fluctuation in the frequency produced by the oscillator due to electrical or physical changes in the constants of the parameters.

It is therefore one purpose of the present invention to provide an ultra high frequency oscillator which is stable in operation and which will supply a fixed fundamental frequency as determined by the physical dimensions of the oscillator alone.

Another purpose of the present invention resides in the provision of means whereby the oscillator may supply considerable power and the further provision of means whereby various agencies may be conveniently used to prevent the oscillator from becoming overheated, even though considerable power output is supplied by the oscillator.

Another advantage of the present invention resides in the provision of means whereby the oscillator may be cooled through the circulation of some cooling medium such as water, the cooling medium in some instances being readily applied both to the interior and the exterior of the oscillator tube proper.

A still further advantage of the present invention resides in the fact that by reason of the new and novel construction of one form of the high frequency oscillator, the envelope may be metallic and furthermore, may be maintained at ground potential.

Still another purpose of the present invention resides in the provision of means whereby an oscillator, constructed in accordance with the present invention, may be positioned within a hermetically sealed glass or ceramic envelope.

Another purpose of the present invention resides in the provision of a hot cathode from which electrons may be derived and the control of the West Lafayette, Ind.

1939, Serial No. 286,301

number of electrons emitted from the cathode by means of a grid arrangement.

Another advantage of the present invention resides in the fact that the oscillator constructed in accordance with this invention may be used to develop frequencies of the order of from 3x to at least the order of 3x10 cycles per second. These frequencies correspond in wave length to from one meter to ten centimeters respectively.

A still further purpose of the present invention resides in the provision of means whereby the frequencies delivered by the oscillator may be readily applied to a high frequency transmission line in order that the frequencies may later be utilized in the manner desired.

Still another purpose of the present invention resides in the provision of means whereby the amplitude of the oscillations produced by the oscillator may be readily controlled so that the oscillations produced by the oscillator may be amplitude modulated in any desired manner.

Still other purposes and advantages of the present invention will become more apparent to those skilled in the art from a reading of the following specification and claims, particularly when considered with the drawing, wherein:

Figure 1 represents one form of the present invention and,

Figure 2 represents a modification of the invention. I

Referring now to the drawing, and particularly to Figure 1, the ultra high frequency oscillator comprises a pair of tubular members in and i2 of different diameters, the one having the smaller diameter being positioned within and coaxial with respect to the one having the larger diameter. These two cylinders are hermetically sealed with respect to each other by annular end members l4 and it. The tubular member l2 may exceed the length of the tubular member l0 and accordingly extend beyond the planes of the annular end members it and i6 for a purpose which will be explained later. Within the envelope and within the region between the two tubular members are positioned a source of electrons and a control electrode. The source of electrons or the cathode is in the form of a plurality of electrical current conducting filaments it which are connected across the support conductors and 22. The cathode conductors are spaced concentrically between the two tubular members Ill and I2 and are positioned substantially midway between the annular end members it and IS. The support conductors 2| and 22 expand in a direction parallel with the tubular members and are in turn electrically connected to conductors 24 and 26 which extend to the outside of the oscillator tube through a glass or ceramic seal 30, in order that the interior of the tube may be hermetically sealed with respect to the outside. The conductors 24 and 26 also function as mechanical supports for the filament cathode conductors l8. The glass or ceramic seal member 30 is fused to a metallic collar 32, the end portion of which is reduced in thickness in order to afford sufficient flexibility to compensate for the different coeflicients of expansion between the metallic c01- lar and the ceramic seal. The collar 32 is attached to the tubular members In in any appropriate manner such as by welding or brazing.

For controlling the flow of electrons from the cathode l8 to the tubular members, two cylindrically shaped control electrode structures are provided. The outer control electrode comprises a series of conductors 34 which are supported by bars 36, while the inner grid structure comprises a plurality of conductors 38 which are supported by the bars 40. The supporting bars 36 and 40 are electrically connected by a plurality of bridging members 42 (one of which is shown in the drawing) and both the inner and the outer grid electrodes are supported by conductor 44. This conductor 44 extends outside the oscillator tube and in order that the interior of the tube may be maintained hermetically sealed, conductor 44 is passed through a glass or ceramic seal member 46, the seal member cooperating with a collar 48 in a manner similar to that described above with respect to the seal 30 and the collar 32.

The ultra high frequency oscillations as produced by the oscillator are supplied to a transmission line which may be used to feed an antenna such asa di-pole (not shown) or any other apparatus where ultra high frequency oscillations of a fixed frequency are desired.

52 is electrically connected to the tubular member ID while the conductor 54 extends through a ceramic seal 56 and connects to the inner tubular member l2 at a to a very low degree.

The space between the two tubular members 10 and i2 is exhausted during the making of the oscillator, the seal-ofi tip being indicated at 50.

63. The cathode conductors I! are maintained at proper operating temperature to afford a production of electrons by means of current derived from the source of potential 64. The control electrodes are normally maintained slightly negative with respect to the cathode and the amount of this negative potential may be determined by a variable potentiometer which is connected in parallel with a source of potential 68, the positive terminal of which is connected to the cathode. By reason of this circuit arrangement electrons which are emitted from the cathode 18 are controlled in intensity by the potential of the control electrodes and the electrons which are permitted to escape from the cathode are collected by the tubular members In and I2, these members operating as anodes. As may be seen from the drawing, the electrons cathode through the inner control electrode 38 to the tubular member l2.

The frequency supplied by the oscillator, for all practical purposes, is determined by the internal dimensions of the oscillator, the wave length of the oscillations being equal to twice the distance between the inside surfaces of the end members I4 and I6. In other words, the distance from the center of the tube to the inner surface of either end wall is equivalent to one-fourth of the wave length of the oscillations produced by the tube. When the tube is in operation, a standing current wave is present on the inner surface of the tube extending in each direction from the center of each tubular member l0 and 12 to the end of the tube and back again to the center of the tubular members.

When the tube is to be operated, the cathode conductors H! are heated to a suflicient temperature to produce electrons and upon the application of anode potential to the tube these electrons are, for the purpose of explanation, attracted to the tubular member ID. This surge of electrons to the tubular member I 0 causes a slight difference of potential to exist between the tubular member in and the tubular member 12 and as a result a certain amount of current will flow from the center portion of the tubular member ID to each annular end Wall, and back to the center of the tube along the tubular member l2. Furthermore, the electronic current from the cathode tuate rapidly between the inner and outer tubu- Since the frequency of the oscillations proaaienvo duced by the tube are determined solely by the internal dimensions thereof. and since therate of progression of the standing wave along the inside surface of the oscillator tube proper is relatively fixed, then the length of time which transpires between each oscillation of the standing current wave is definitely determined. In order that the electronic current flow from the cathode It may also oscillate in synchronism with the standing wave oscillations and in proper phase relationship with respect thereto some variation or adjustment of the potential diirerence between the cathode and the tubular members II and I! may be necessary. The proper operating potential for most eillcient operation may be readily determined through experimentation.

The tube is initially set into oscillation through some possible misalignment of the electrodes contained within the tube or oscillation may actually be initiated through transient disturbances which accompany the switching operation to place the tube in operating condition. In view of the fact that the tube has an inherent tendency to oscillate no specific means need be provided to instigate the oscillations since these oscillations will start immediately upon the application of operating potentials to the electrodes of the tube. At each oscillation of the standing current wave additional electrons are added from the electronic stream and the oscillation of the standing current wave is therefore maintained and increased in intensity until an optimum value is reached. With respect to the proper operating potential which must be maintained between the cathode and the anodes or the tubular members ill and II,

this choice of potential affects only the power output of the tube since the frequency supplied by the tube is not affected by this potential but is rather determined by the physical dimensions of the oscillator tube per se.

In the above example of operation of the device it was assumed that, upon the application of potentials to the oscillator, the tube would immediately be placed in an oscillating condition. Whether a preponderance of electrons is initially applied to the tubular member III or the tubular member I! is immaterial, since in either case oscillations will be initiated and sustained. Furthermore, in view of the high Q of the tube, no means are required for initially establishing oscillations since the transient conditions and disturbances which accompany the initial energization of the tube are entirely suilicient to establish initial oscillation, as explained above. The Q of the ultra high frequency oscillator tube constructed in accordance with this invention is quite large, and is of the order of several thousand. This is by reason of the fact that the inductance of the tube times the frequency generated thereby is large as compared to the resistances and losses thereof since From this equation it may be seen that if the frequency is of the order of that indicated earlier in this specification, the Q will be quite large since the resistance and losses are relatively small.

Inasmuch as the surfaces of the tube which are exposed to atmospheric pressure may be constantly maintained at zero or ground potential, it is possible to immerse the tube in water or some other liquid or fluid cooling bath. Furthermore, it is entirely possible to circulate water through the bore of the inner tubular member I! by connecting a hose or other conduit to either end thereof.

As stated above, the wave length of the irequency supplied by the oscillator is for practical apart various amounts as determined by the end I wall dimensions. There is, however, a more or less optimum value for the size of the annular end wall members and the spacing of the tubular members. This value may be determined either experimentally or through calculation. If the difierential between the radii of the end wall members I4 and it (that is, the spacing of the two tubular members Ill and I2) is increased, then obviously greater energizing potentials must be applied between the cathode i8 and the tubular members l0 and [2. ,Such increase in potential must be applied by reason of the fact that the transit time of the electrons from the cathode l8 to the one or the other of the tubular members II and I2 should, for most eilicient operation, correspond exactly to the transit time required for the standing wave to make one-half oscillation. v

The thickness of the tubular members l0 and II, as well as the end members I4 and I6 is not vital since, as stated above, the current of the standing wave is confined to the inner surfaces of oscillator tube. The thickness of the envelope is therefore determined by the size of the oscillator and the amount of mechanical strength necessary to withstand the atmospheric pressure to which the tube is subjected when exhausted.

The axial lengths of the cathode structure as well as of the grid electrodes is not particularly vital but should not be excessive sincefor best operation the electrons, as supplied to the tubular members It and I2,'should be collected at substantially the central portion ofeach of these members. If, on the other hand, the length of the cathode and grid structures is too reduced, the available power output of the oscillator may also be correspondingly reduced.

In Fig. 2 is shown a modification of the oscillator shown in Fig. i and in this figure, the active elements of the oscillator correspond to half of the elements shown in Fig. 1. In Fig. 2 the oscillator is positioned within a glass or ceramic envelope 80. The oscillator comprises an outside tubular member I0 and an inner tubular member 12'. One end of each of the tubular members is attached to a single end wall member It for maintaining the tubular members in coaxial spaced relationship and for establishing electrical contact between the two tubular members. The other end of the tubular members remains open. Positioned at the open end of the tubular members is a cathode comprising cathode filament wires l8. Surrounding the cathode is an outer grid electrode 34 and an inner grid electrode 38'. The cathode filaments are supported by means of lead-in wires 24 and 26' as in Fig. 1, whereas the grid electrodes are supported by means of the conductor 44'. The inner and outer tubular members are maintained at a positive potential with respect to the cathode and this potential is applied to the tubular members by means of conductor 82. The two tubular members comprising the'oscillator are maintained in position within the glass envelope by means of an internal extension 84 which is integral with the glass envelope and in order that the tubular member I2 may firmly contact the extension 84 a plurality of spring members 86 are provided, these spring members being permanently attached to the inside of the tubular member l2 in such a manner that they may cooperate with the tubular extension 84. The conductor 82 which supplies the positive potential to the cylindrical members assists in preventing movement of the open ends of the tubular members.

For providing an output circuit for the oscillator a concentric cable 50' is provided which comprises an external tubular member 52 and an internal concentric conductor 54'. The internal conductor 54' is attached to the tubular member l2 a short distance from the closed end thereof, the distance being determined in accordance with the impedance necessary to match the impedance of the output circuit. At the point where the conductor 54 passes through the end wall IS, a ceramic member 81 is provided for hermetically sealing the ceramic oscillator envelope housing 80. In order to complete the seal, a collar member 88 is attached to the tubular member 52' of the concentric cable and the glass housing is fused to this collar. It may be seen, therefore, that the interior of the ceramic housing may be exhausted in order that a very low pressure may be maintained for the oscillator.

The operation of the device shown in Fig. 2 is substantially identical with the operation of the device shown in Fig. 1 and upon energization of the tube the flow of the electric current from the cathode l8 will be caused to oscillate between the tubular members Ill and i2. Simultaneously, a standing current wave will be caused to flow on the inner and outer surfaces of the tubular members l and i2 respectively, as well as over the inside surface of the end wall For energizing the oscillator the filament cathode I8 is supplied with current from the source of potential 84' and the grid electrodes are maintained slightly negative with respect to the cathode by an amount determined by the setting of the potentiometer 66 which is connected across the source of potential $8.

The oscillator shown in Figs. 1 and 2 may be used merely as a source of ultra high frequency oscillations alone, or if the oscillator is used to supply a carrier frequency to a transmitting antenna by way of a transmission line, then it might become desirable to modulate the ultra high frequency oscillations by a variable frequency such as by the video or picture frequencies which originate at a television transmitting station. Such modulating frequencies, if derived from a television camera, may vary from zero to some 4 or 5 megacycles per second. Amplitude modulation of the high frequency oscillations may be produced in a very convenient manner. In Fig. 1 an inductive member is included in circuit with the control electrodes and electromagnetically associated with this inductive member is a winding 12 upon which may be impressed the modulating frequency. As the modulating frequency is induced in the inductive member 10 by reason of the mutual inductance of the windings l0 and 72, the control electrodes 34 and 38 are caused to vary in potential with respect to the cathode l8 and accordingly the intensity of the oscillations produced by the oscillator is varied so that the oscillations are amplitude modulated in accordance with the signals applied to the control electrodes. In Fig. 2 the modulating potential may be applied to the control electrodes by way of the condenser 90 so that the potential of the control electrodes with respect to the cathode may be varied in accordance with the applied signals. In this instance, as in the case of Fig. 1, the amplitude of the produced oscillations will be caused to be varied in accordance with the potentials applied to the control electrodes. In view of the very high Q of the oscillator shown in Figs. 1 and 2, very little power is required to swing the control electrodes so that relatively low power signal amplifying tubes may be used to supply sufiicient modulating potentials to the control electrodes of the oscillator.

Inasmuch as the impedance of a di-pole antenna is normally less than 100 ohms and generally of the order of 72 ohms (which impedance is somewhat independent of wave length at which the antenna is operated) proper impedance matching between the transmission line 50 or 50' and the antenna or load circuit is necessary and desirable so that the impedance of the transmission line should be substantially equivalent to the impedance of the antenna. Furthermore, for complete impedance matching the connection of the conductor 54 to the tubular member l2 should be at such a point with respect to the end of the oscillator that the impedance at the point of connection will also be equivalent to the impedance of the transmission line (coaxial cable) and to the di-pole antenna. Such a connection will obviously be relatively adjacent the end of the oscillator tube, since the impedance of the oscillator at the plane of the end wall thereof is zero, the impedance increasing approximately to infinity at a point midway between the ends of the oscillator shown in Fig. l or at the open ends of the tubular members of the oscillator shown in Fig. 2. The exact location of this connection may be determined by mathematical calculation, by experimentation or by graphic analysis.

An ultra high frequency oscillator of the type shown and described herein is also shown and described in U. S. patent application Serial #263,112, filed March 21, 1939, by R. H. George and H. J. Heim.

From the above it may be seen that an improved ultra high irequency oscillator has been developed which is inherently stable in operation since the frequency delivered by the oscillator is entirely a function of the internal length thereof, which, of course, is fixed and constant. The oscillator includes no external circuits other than those necessary to supply power thereto, and

all of the elements necessary to produce oscillations are included within the tube envelope. Furthermore, even though the oscillator is capable of generating high frequency oscillations of the order referred to above, the oscillator is still of such physical dimensions as to permit it to supply considerable power and as to permit it to be conveniently and practically constructed without the exercise of an excessive degree of technical or mechanical skill. The principal portion of the apparatus to which attention must be directed in the process of construction is the internal length of the tube which, as stated above, determines the frequency at which the tube oscillates.

Also, it may be seen that oscillation devices of this type may be constructed to produce a wide range of frequencies, since an oscillator tube having an internal length of 5 cm. will produce oscillations of the order of 3 10 cycles per second. Such a frequency is, of course, not necessarily the upper limit of a device constructedin accordance with this invention, since it is feasible to construct a tube having an internal length of less than 5 centimeters. The low frequency extreme to which such a device may be operated is determined solely by the practical physical length which may be used.

In view of the construction of the oscillator shown in Fig. 1, a very large quantity of power may be derived therefrom, it being entirely possible to increase the amount of power by cooling the tube through the use of some fluid cooling medium. The use of a cooling fluid at ground potential is permissible, in view of the fact that the external surface of the oscillator may be maintained at ground potential. The fact that a cooling fluid may be placed in intimate contact with the metallic tube envelope is advantageous since rapid cooling results. and furthermore, by controlling the temperature of the cooling medium the length of the tube may be controlled within very close limits, thereby compensating for any small errors in the length of the tube due to construction, so that the tube may be made to operate at exactly the desired frequency much in the manner in which the oscillations of a crystal oscillator are accurately controlled. The length of the tube may, therefore, be varied slightly as a function of temperature by reason of the thermal coemcient of expansion of the metal of which the device is made (preferably copper). The device shown in Fig. 2 being different in construction from that shown in Fig. 1 cannot be placed in direct contact with a cooling medium by reason of the existence of the glass housing 80, but where excessive power is not necessary, the device shown in this figure may readily be used. Furthermore, considerable radiation from the oscillator shown in Fig. 2 is possible, so that even though direct cooling mediums may not be applied to the metallic portions of the oscillator, considerable quantities of power may still be derived therefrom. In view of the fact that the tubular members ill and I! are not subjected toatmospheric pressure, the material of which these members (as well as the end members I6) is constructed may be much thinner than the corresponding elements of the device shown in Fig. 1. By constructing the tubular members ill and I! of the very thin material, the weight of the oscillator may be reduced and the possibility of damage through vibration or mechanical shock may be materially lessened.

In view of the construction of the oscillator described above, no additional shield means for shielding the oscillator need be provided. Accordingly, no apparatus which is situated near the oscillator will be affected thereby due to any extraneous or surrounding flelds, inasmuch as no such fields can exist by reason of the complete self shielding construction. This is particularly true of the device disclosed in Fig. 1 since the oscillator is completely enclosed within a metallic envelope, except for the ceramic seals which are, of course, relatively small. Furthermore, by reason of the unique construction of the device a transmission line or output circuit may be very closely coupled to the oscillator so that losses due to such coupling may be reduced to a minimum.

Although the device is shown more or less specifically in form in the drawing, it is to be understood that various other modes of construction may be employed such as difl'erent means for supporting the electrodes within the oscillator or the replacement of the fllament type cathode by an indirectly heated type.

Various modifications and alterations may be made in the present invention without departing from the spirit and scope thereof, and it is desired that any and all such modifications be considered within the purview of the present invention except as limited by the hereinafter appended claims.

I claim:

1. An ultra high frequency oscillator comprising a pair of conducting tubular members of different diameters, a pair of conducting annular end members for maintaining the tubular members coaxially and concentrically spaced to produce an hermetically sealed space between the members, a cylindrical source of electrons including a heated cathode positioned concentrically between the tubular members and substantially midway between the annular end members, a cylindrical grid-like control electrode positioned on opposite sides of the source of electrons, means for maintaining a high direct current potential between the tubular members and the source of electrons, means for maintaining the control electrode negative with respect to the source of electrons, an output circuit including a coaxial cable comprising an internal and an external conductor, means for connecting the external conductor to the tubular member having the larger diameter, and means for connecting the internal conductor to the other tubular member at a point near one end thereof.

2. An ultra high frequency oscillator comprising a pair of tubular members of different diameters, a pair of annular end members for maintaining the tubular members coaxially and concentrically spaced to provide an hermetically sealed space between the members, a source of electrons comprising a cathode positioned between the tubular members and substantially midway between the annular end members, a grid-like control electrode positioned on oppo site sides of said cathode, means for maintaining a high potential between the tubular members and said cathode, means for maintaining the control electrode negative with respect to said cathode, an output circuit including a coaxial cable comprising an internal and an external conduEFcYr, means for connecting the external conductor to the tubular member having the larger diameter, and means for connecting the internal conductor to the other tubular member at a point near one end thereof.

3. An ultra high frequency oscillator comprising a pair of conducting tubular members of different diameters, a pair of conducting end members for maintaining the pair of tubular members coaxially and concentrically spaced, a cylindrical cathode member, means for positioning the cathode coaxially with respect to the tubular members and substantially equi-distant between the end members, a control electrode or grid structure of cylindrical form spaced from each side of the cathode and concentrically positioned with respect thereto, means for applying a direct current potential between the tubular members and the cathode, means for maintaining the control electrode negative with respect to the cathode, an output circuit including a coaxial cable comprising an internal and an ex-' ternal conductor, means for connecting the external conductor to one of the tubular members, and means for connecting the internal conductor to the other tubular member.

4. An ultra high frequency oscillator comprising a pair of tubular members of diiferent d1- ameters, a pair of end members for maintaining the pair of tubular members coaxially and concentrically spaced, a cathode member, means for positioning the cathode between the tubular members and substantially equidistant between the end members, a control electrode structure surrounding said cathode and spaced therefrom, means for applying a potential between the tubular members and said cathode, means for maintaining the control electrode at a slightly different potential with respect to said cathode, an output circuit including a coaxial cable comprising a pair of conductors, means for connecting one of the conductors to one of the tubular members, and means for connecting the other of the conductors to the other tubular member.

5. An ultra high frequency oscillator comprising a pair of conducting tubular members of different diameters, a pair of conducting end members for maintaining the tubular members coaxially and concentrically spaced to provide an hermetically sealed space between the members, a cylindrical cathode electrode, means for positioning the cathode in the hermetically sealed space between the tubular members, a grid-like control electrode assembly positioned to surround the cathode electrode, said cathode and surrounding control electrode being positioned substantially centrally with respect to the end members, means including a source of high potential for maintaining a potential difference between the tubular members and said cathode, means for maintaining a predetermined potential relationship between the control electrode and the cathode, an output circuit including a coaxial cable comprising an internal and an external conductor, means for connecting the external conductor to one of the tubular members, and means for connecting the internal conductor to the other tubular member.

6. An ultra high frequency oscillator comprising a pair of tubular members of different diameters, a pair of end members for maintaining the tubular members coaxially and concentrically spaced to provide an hermetically sealed space between the tubular members, a cathode electrode, means for positioning said cathode in the hermetically sealed space between the tubular members, a grid-like control electrode assembly positioned to surround said cathode, said cathode and surrounding control electrode being positioned substantially centrally with respect to said end members, means including a source of high potential for maintaining a potential diiierence between the tubular members and said cathode, and means for maintaining a predetermined potential relationship between the control electrode and the cathode.

7. An ultra high frequency oscillator comprising a pair of tubular members of different diameters, a pair of end members for maintaining the tubular members coaxially and concentrically spaced to provide an hermetically sealed space between the members, a cathode electrode, means for positioning the cathode in the hermetically sealed space between the tubular members, a grid-like control electrode assembly positioned to surround said cathode, said cathode and surrounding control electrode being positioned substantially centrally with respect to said end members, means including a source of high potential for maintaining a potential difference between the tubular members and said cathode,

means for maintaining a predetermined potential relationship between the control electrode and the cathode, and means to modulate the potential relationship between the control electrode and the cathode.

8. An ultra high frequency oscillator comprising a pair of conducting tubular members of different diameters, a pair of conducting annular end members for maintaining the tubular members coaxially and concentrically spaced with respect to each other to provide an hermetically sealed space between the members, a cylindrical cathode electrode for providing a source of electrons, means for positioning said cathode coaxially between the tubular members and substantially midway between the end members, an electron pervious control electrode surrounding said cathode, means for applying a source of high voltage direct current potential between the tubular members and the cathode, means for maintaining a predetermined potential relationship between the control electrode and the cathode, and an output circuit connected to the tubular members.

9. An ultra high frequency oscillator comprising a pair of tubular members of different diameters, a pair of annular end members for maintaining the tubular members coaxially and concentrically spaced with respect to each other to provide an hermetically sealed space between the members, a cathode electrode for providing a source of electrons, means for positioning said cathode between the tubular members and substantially midway between the end members, a control electrode surrounding said cathode, means for applying a source of high voltage potential between the tubular members and said cathode, means for maintaining a predetermined potential relationship between the controlelectrode and said cathode, and means to modulate the potential relationship.

10. An ultra high frequency oscillator comprising a pair of tubular members, a pair of end members for maintaining the tubular members coaxially and concentrically spaced with respect to each other in order to provide an hermetically sealed space, a cathode electrode, means for positioning said electrode between the tubular members and the end members, an electron pervious control electrode surrounding said cathode electrode, means for impressing a direct current potential source between the tubular members and said cathode, means for applying varying potentials to the control electrode, and an output circuit connected to the tubular members.

11. An ultra high frequency oscillator comprising a pair of tubular members, a pair of end members for maintaining the tubular members coaxially and concentrically spaced with respect to each other in order to provide an hermetically sealed envelope, a cathode electrode, means for positioning said cathode electrode within the envelope, an electron pervious control electrode surrounding said cathode, means for impressing a high potential between the envelope and said cathode, means for applying a potential to the control electrode, and means to modulate the applied potential.

12. An ultra high frequency oscillator comprising a pair of conducting tubular members, a pair of conducting end members for maintaining the tubular members coaxially and concentrically spaced with respect to each other, a cylindrical cathode electrode for providing a source of electrons, means for positioning said cathode concentrically between the tubular members, a cylindrical control electrode surrounding said cathode, means for impressing a direct current potential source between the tubular members and said cathode, means for maintaining a predetermined potential relationship between the control electrode and said cathode, means to modulate the potential relationship, and an output circuit connected to the tubular members.

13. An ultra high frequency oscillator comprising a pair of tubular members, a pair of end members for maintaining the tubular members coaxially and concentrically spaced with respect to each other, a cathode electrode for providin a source of electrons, means for positioning said cathode between the tubular members, a control electrode surrounding said cathode, means for impressing a direct current potential source between the tubular members and said cathode, means for maintaining a predetermined potential relationship between the control electrode and said cathode, and means to modulate the potential relationship.

14. An ultra high frequency oscillator comprising a pair of conducting tubular members, a pair of conducting end members adapted to maintain the tubular members coaxially and concentrically spaced, a cathode electrode for providing a source of electrons, means to position said cathode electrode between the tubular members, an electron pervious control electrode surrounding said cathode, means for maintaining said tubular members positive with respect to said cathode, means for maintaining said control electrode negative by a predetermined amount with respect to said cathode, and an output circuit connected to said tubular members.

15. An ultra high frequency oscillator comprising a pair of tubular members, a pair of end members adapted to maintain the tubular members coaxially and concentrically spaced, a cathode electrode, means to position said cathode between the tubular members, an electron pervious controlelectrode surrounding said cathode,

means to maintain said tubular members positive with respect to said cathode, means to maintain said control electrode negative with respective to said cathode.

16. An ultra high frequency oscillator comprising a casing having an inner and an outer tubular wall member, end members for providing an hermetically sailed space between the tubular members, a cylindrical cathode electrode for providing a source of electrons, means for concentrically positioning said cathode between the wall members, an electron pervious control electrode surrounding said control electrode, means for maintaining said wall members positive with respect to said cathode, means for maintaining a predetermined potential relationship between the control electrode and said cathode, and means to modulate the potential relationship.

17. An ultra high frequency oscillator comprising a casing having an inner and an outer tubular wall member, end members for providing an hermetically sealed space between the tubular members, a cathode electrode, means for positioning said cathode between the wall members, an electron pervious control electrode surrounding said control electrode, means to maintain said wall members positive with respect to said cathode, and means to maintain a predetermined potential relationship between the control electrode and said cathode.

18. An ultra high frequency oscillator comprising a casing having an inner and an outer wall member, together with end members for providing an hermetically sealed space between the members, a cathode electrode positioned between the members, a control electrode grid structure surrounding said cathode, means for maintaining said wall members positive with respect to said cathode, means !or applying a predetermined potential difference between said control electrode and said cathode, and an output circuit connected to the wall members.

19. An ultra high frequency oscillator comprising a casing having an inner and an outer wall member, together with end members for providing an hermetically sealed envelope, a cathode electrode positioned within the envelope, a control electrode grid structure surrounding said cathode, means for maintaining the envelope positive with respect to said cathode, and means for applying a modulated potential difference between said control electrode and said cathode.

20. An ultra high frequency oscillator comprising a pair of electrodes at least one of which forms the side wall of a casing, closure means associated with said electrodes for providing an hermetically sealed space between the electrodes, a cathode electrode, means for positioning said cathode between the first-named electrodes, an electron pervious control electrode surrounding said cathode, means for maintaining a high potential difference between said first-named electrodes and said cathode, and means for maintaining a predetermined potential relationship between the control electrode and said cathode.

21. An ultra high frequency oscillator comprising a pair of electrodes at least one of which forms the entire side wall of a casing, closure means associated with said electrodes for providing an hermetically sealed space between the electrodes, a cylindrical cathode electrode for providing a source of electrons, means for concentrically positioning said cathode between the first-named electrodes, an electron pervious control electrode surrounding said cathode, means for maintaining a high potential difierence between said first-named electrodes and said cathode, and means for maintaining a predetermined potential relationship between the control electrode and the cathode.

22. An ultra high frequency oscillator comprising a casing having a pair of coaxially and concentrically spaced tubular conducting members and an end wall adapted to electrically connect one end of each of the tubular members, means whereby a vacuum may be maintained by the members, a cylindrical cathode electrode for providing a source of electrons concentrically positioned between the members, a control electrode surrounding said cathode, means for maintaining a high potential difierence between a cathode and the members, means for maintaining a predetermined potential relationship between the control electrode and the cathode, and an output circuit connected to said members.

23. An ultra high frequency oscillator comprising a casing having a pair of coaxially and concentrically spaced members and an end wall adapted to electrically connect one end of each of the members, means whereby a vacuum may be maintained by the members, a cathode electrode positioned between the members, a control electrode surrounding said cathode, means for maintaining a potential difference between a cathode and the members, and means for mainrounding said cathode, means for maintaining the envelope positive with respect to said cathode, means ior maintaining said control electrode negative with respect to said cathode,

means to modulate the potential applied to the 5 control electrode, and an output circuit including a concentric cable connected to said envelope.

ROSCOE H. GEORGE. 

